Halogen incandescent lamps are frequently used for illumination, usually in combination with reflectors. Such lamps may be coated with an infrared reflecting layer on the lamp bulb to decrease the power rating of the lamp, while still retaining high filament temperature. The lamp bulb is shaped, preferably, exactly or at least essentially in the shape of an ellipsoid.
A manufacturing process to make halogen incandescent lamps of the general type to which the present invention relates is described in U.S. Pat. No. 4,756,701, Danko et al. In accordance with this method, the future lamp bulb is formed by preforming a glass tube at one end to have cup shape, leaving however an opening at the apex of the cup. A pumping tube is melted into that opening. The subassembly is then placed into a mold which completely surrounds it, leaving however the end of the pumping tube free. The bulb is fitted against the inner contour of the mold by inserting an inert gas, with pressure, through the pumping tube. The major portion of the bulb, thus, receives its final shape in this step, and particularly in the region of the cupped end and the adjacent zone of the bulb. A filament mount, together with the filament, is then inserted, and this second subassembly is placed into a pinch mold, so that the second end of the lamp bulb can be closed off with a pinch seal, at the same time forming the remaining portion of the lamp bulb. The lamp bulb is then evacuated through the pumping tube, filled, and the pumping tube is severed and the opening tipped off by melting.
This method requires several individual steps which are time-consuming, so that the overall method becomes expensive. Upon shaping of the bulb, a region adjacent the cupped end is left open, so that, adjacent the molten-in connection of the pumping tube, the shape of the bulb may not always have the desired form.